<template>
  <!-- text-sm/[30px] 表示文字小号，行高为 30px -->
  <div v-if="titles && titles.length > 0"
       class="sticky top-[5.5rem] text-sm/[30px] w-full p-5 mb-3 bg-white border border-gray-200 rounded-lg dark:bg-gray-800 dark:border-gray-700">
    <!-- 目录标题 -->
    <h2 class="flex items-center mb-2 font-bold text-gray-900 uppercase dark:text-white">
      <!-- 目录图标 -->
      <svg t="1699441758495" class="icon w-3.5 h-3.5 mr-2" viewBox="0 0 1024 1024" version="1.1"
           xmlns="http://www.w3.org/2000/svg" p-id="4043" width="200" height="200">
        <path
            d="M857.6 25.6a76.8 76.8 0 0 1 76.8 76.8v819.2a76.8 76.8 0 0 1-76.8 76.8H166.4a76.8 76.8 0 0 1-76.8-76.8V102.4a76.8 76.8 0 0 1 76.8-76.8h691.2z m-102.4 678.4H473.6l-2.2528 0.064a38.4 38.4 0 0 0 0 76.672L473.6 780.8h281.6l2.2528-0.064a38.4 38.4 0 0 0 0-76.672L755.2 704z m0-230.4H473.6l-2.2528 0.064a38.4 38.4 0 0 0 0 76.672L473.6 550.4h281.6l2.2528-0.064a38.4 38.4 0 0 0 0-76.672L755.2 473.6z m0-230.4H473.6l-2.2528 0.064a38.4 38.4 0 0 0 0 76.672L473.6 320h281.6l2.2528-0.064a38.4 38.4 0 0 0 0-76.672L755.2 243.2z"
            fill="#6B57FE" p-id="4044"></path>
        <path
            d="M281.6 691.2a51.2 51.2 0 1 1 0 102.4 51.2 51.2 0 0 1 0-102.4z m0-230.4a51.2 51.2 0 1 1 0 102.4 51.2 51.2 0 0 1 0-102.4z m0-230.4a51.2 51.2 0 1 1 0 102.4 51.2 51.2 0 0 1 0-102.4z"
            fill="#FFBA00" p-id="4045"></path>
      </svg>
      文章目录
    </h2>
    <div class="border-l-2 border-gray-200">
      <ul>
        <!-- 二级标题 -->
        <li v-for="(h2, index) in titles" :key="index" class="pl-5" :class="[h2.index == activeHeadingIndex ? 'active text-sky-600 border-l-2 border-sky-600 font-bold' : 'text-gray-500 font-normal']">
          <span @click="scrollToView(h2.offsetTop)">{{ h2.text }}</span>
          <!-- 三级标题 -->
          <ul v-if="h2.children && h2.children.length > 0">
            <li v-for="(h3, index2) in h2.children" :key="index2" class="pl-5" :class="[h3.index == activeHeadingIndex ? 'active text-sky-600 border-l-2 border-sky-600 font-bold' : 'text-gray-500 font-normal']">
              <span @click="scrollToView(h3.offsetTop)">{{ h3.text }}</span>
            </li>
          </ul>
        </li>
      </ul>
    </div>
  </div>
</template>

<script setup>
import { ref, onMounted, onBeforeUnmount } from 'vue'

// 响应式的目录数据
const titles = ref([])
onMounted(() => {
  // 通过 .artilce-content 样式来获取父级 div
  const container = document.querySelector('.article-content')

  // 使用 MutationObserver 监视 DOM 的变化
  const observer = new MutationObserver(mutationsList => {
    for (let mutation of mutationsList) {
      if (mutation.type === 'childList') {
        // 先清空目录缓存数据
        titles.value = []
        // 监听所有图片的加载事件
        const images = container.querySelectorAll('img');
        images.forEach(img => {
          img.addEventListener('load', () => {
            // 图片加载完成后重新计算标题的 offsetTop
            initTocData(container)
          })
        })

        // 添加滚动事件监听
        window.addEventListener('scroll', handleContentScroll);
      }
    }
  })

  // 配置监视子节点的变化
  const config = { childList: true, subtree: true }
  // 开始观察正文 div 的内容变化
  observer.observe(container, config)
})

// 记录当前被选中的标题下标
const activeHeadingIndex = ref(-1)
// 处理滚动事件
function handleContentScroll() {
  // 当前的滚动位置
  let scrollY = window.scrollY
  // 循环目录
  titles.value.forEach(title => {
    // 获取每个标题的 offset
    let offsetTop = title.offsetTop
    // 如果当前位置大于等于标题位置，则标记选中，记录被选中标题的下标
    if (scrollY >= offsetTop) {
      activeHeadingIndex.value = title.index
    }

    // 处理3级标题, 同样的逻辑
    let children = title.children
    if (children && children.length > 0) {
      children.forEach(child => {
        let childOffsetTop = child.offsetTop
        if (scrollY >= childOffsetTop) {
          activeHeadingIndex.value = child.index
        }
      })
    }
  })
}

// 移除滚动监听
onBeforeUnmount(() => window.removeEventListener('scroll', handleContentScroll))

// 滚动到指定的位置
function scrollToView(offsetTop) {
  window.scrollTo({ top: offsetTop, behavior: "smooth" });
}

// 初始化标题数据
function initTocData(container) {
  // 只提取二级、三级标题
  let levels = ['h2', 'h3']
  let headings = container.querySelectorAll(levels)

  console.log(headings)

  // 存放组装后的目录标题数据
  let titlesArr = []

  // 下标
  let index = 1
  headings.forEach(heading => {
    // 标题等级， h2 -> 级别 2 ； h3 -> 级别3
    let headingLevel = parseInt(heading.tagName.substring(1))
    // 标题文字
    let headingText = heading.innerText
    // 标题的位置（距离顶部的距离）
    let offsetTop = heading.offsetTop - 95

    if (headingLevel === 2) { // 二级标题
      titlesArr.push({
        index,
        level: headingLevel,
        text: headingText,
        offsetTop,
        children: [] // 二级标题下的子标题
      })
    } else { // 三级标题
      // 父级标题
      let parentHeading = titlesArr[titlesArr.length - 1]
      // 设置父级标题的 children
      parentHeading.children.push({
        index,
        level: headingLevel,
        text: headingText,
        offsetTop
      })
    }
    // 下标 +1
    index++
  })

  // 设置数据
  titles.value = titlesArr
}
</script>
